Threshold Test Printout Formats; Reliability Indices - Zeiss HUMPHREY 720i User Manual

7-4
THRESHOLD TEST
PRINTOUT FORMATS

Reliability indices

Foveal threshold
REV. B 02/03 PN 51680-1
STATPAC ANALYSIS & PRINTING RESULTS
Until this point, the User's Guide has focused on the use and operation of the HFA II. In
attempting to explain the information provided on printouts, however, we must enter the realm
of interpretation of field results.
Humphrey Field Analyzer printouts have always included reliability indices to help you
determine the reliability of the patient's responses in interpreting test results. These indices
include fixation losses, false positive errors, and false negative errors. Now, Gaze Tracking can
also be used for reliability information.
The reliability indices for each test appear on the Single Field Analysis, Overview, Glaucoma
Change Probability Analysis, and Three-in-One printout. For Full Threshold and FastPac test
strategies, the HFA II prints "XX" after scores that fall outside the reliability limits used in the
normative database. In addition, STATPAC printouts include the message, "LOW RELIABILITY",
in such cases. For SITA Standard and SITA Fast tests, the "XX" is not printed after high numbers
of false positive or false negative errors, but is printed after fixation losses of 20% or more.
For Full Threshold and FastPac tests, false positive errors, false negative errors, and fixation
losses are printed as a ratio, such as "3/10" . The first number represents the number of
errors committed, while the second number represents the number of times the instrument
checked for each of these errors. In SITA Standard and SITA Fast tests, fixation losses are also
printed as a ratio, but false negative and false positive errors are printed as a percentage, such
as "25%".
The visual fields used in developing STATPAC for the Full Threshold and FastPac strategies were
those of subjects whose reliability indices were within certain limits. Test results showing
fixation loss scores of 20% or more and false positive or false negative errors of 33% or more
were excluded as unreliable. The significance limits thus derived were more restrictive than
they would have been had unreliable test results not been excluded.
Thus, clinical results having poor reliability but for which the STATPAC analysis is normal may
well be normal. Results showing poor reliability and for which the STATPAC analysis is outside
normal limits require careful analysis. Utilize the gaze tracking graph to help determine how
steady patient fixation was during the length of the test.
If the only "XX" on a test result applies to fixation losses and you are sure the patient was
fixating well, the problem may have been poor blind spot positioning rather than poor patient
reliability. High false negative response rates are commonly seen in abnormal fields produced
by completely reliable patients. On the other hand, test results may indeed be unreliable
already at false positive rates lower than the level required to generate the "XX" symbol.
If you used the foveal threshold option when the test was run, the HFA II will print the
measured value just below the test time. When the patient's foveal threshold is significantly
depressed (p < 5%), a probability symbol will appear next to the value shown. This symbol is
identical to those used for the probability plots and indicates the deviation from age normal.
See the following discussions on Total and Pattern deviations for details.
HUMPHREY FIELD ANALYZER II -
i
series